This application claims priority of China 00123144.8, China 01106007.7 and China 01106006.9, filed Oct. 26, 2000, Jan. 5, 2001 and Jan. 5, 2001, respectively, the entire contents of which are hereby incorporated by reference.
The present invention relates to a molecular sieve, especially a mesoporous molecular sieve, and a process for the preparation of the same.
Porous inorganic materials have been widely applied in the catalysis and adsorption separation fields mainly because these materials possess an abundant microporous structure and a larger specific surface area and can provide a great number of acid sites and active adsorption sites. These materials may be roughly classified into amorphous and crystalline and modified pillared-layer materials.
Amorphous materials are important catalyst supports which have been used in industry for many years. The most typical one is amorphous silica-alumina, which is an acidic catalyst and an important support of the reforming catalyst in petrochemical industry. Here xe2x80x9camorphousxe2x80x9d means that the long range is disordered but the short range is generally ordered. The most commonly used methods for characterizing these materials are X-ray diffraction, pore structure analysis and transmission electronic microscopy. The appearance of porous crystalline materials has enlarged the categories of the porous materials, and greatly enriched theory of the porous materials and brought the petrochemical industry a revolution. Especially since the application of the porous crystalline materials in industry results in astonishing economic benefits, people have been carrying out deeper and more perfect investigations on the porous crystalline materials. Porous crystalline materials possess a unique, regular crystalline structure, and each has a pore structure with a definite shape and size. Micropores connect the pores to form xe2x80x9cgiant moleculesxe2x80x9d with abundant pores. Since such a pore structure only permits the molecule with a definite size to pass, this material is referred to as xe2x80x9cmolecular sievexe2x80x9d and this property of molecular sieves has been widely applied. The structure of these molecular sieves, no matter whether they are synthetic or natural, generally has three-dimensional framework structure., Those kinds of molecular sieves only contain Si, Al and O elements are customarily denoted as xe2x80x9czeolitexe2x80x9d. Presently, many kinds of zeolites have been synthesized and widely applied, such as zeolite-A (U.S. Pat. No. 2,882,243), zeolite-X (U.S. Pat. No. 2,882,244), zeolite-Y (U.S. Pat. No. 3,130,007), ZSM-5 (U.S. Pat. No. 3,702,886), ZSM-11 (U.S. Pat. No. 3,709,979), etc. If Al or/and Si in the zeolites are partly or entirely substituted by other atoms, new types of molecular sieves will be formed. Now a variety of new types of molecular sieves have been synthesized and widely applied, such as SAPO series molecular sieves (U.S. Pat. Nos. 6,162,415, 5,370,851, 5,279,810, 5,230,881, 4,440,871, etc.), especially the SAPO-11 molecular sieves (U.S. Pat. Nos. 6,204,426, 6,111,160, 5,833,837, 5,246,566, 4,921,594, 4,499,315). Because these molecular sieves have a unique activity for the isomerization of long-chain alkanes, they are ideal components for the hydroisomerization of the wax in the lubricant oil fraction, and are widely used in the production of the basic oil of the top-grade lubricant oil.
Although the study on molecular sieves is quite mature, the pore diameters of most prepared molecular sieves are below 1.0 nm, and the maximum pore diameter reported in a literature is only 1.3 nm (Davis M E, Saldarriaga C, et al. Nature, 1991, 352: 320). Such molecular sieve still belongs to the micropore one which restricts the reaction of larger molecules. According to the definition of IUPAC, the material with pore diameter below 2 nm belongs to the microporous materials, and the material with pore diameter in the range of 2 nm to 50 nm belongs to the mesoporous material. Based on this definition, most of the prior molecular sieves belong to the microporous molecular sieves. Due to the development of the modern industry, the stricter and stricter environment protection law, and the worldwide tendency for the crude oil to become worse and heavier, it is an urgent task to develop a series of novel materials with super larger pore diameter and specific surface area, stable properties and excellent adsorptive and catalytic performances.
U.S. Pat. Nos. 5,108,725, 5,102,643, 5,098,684, and 5,057,296 disclose a process for synthesizing a mesoporous MCM-41 molecular sieve and its properties. This sort of molecular sieve has a structure of symmetric hexagonal. Its higher surface area, uniform pore distribution, adjustable pore diameter and acidity, accessible active sites, small diffusion resistance, ability to provide favorable space and effective acidic active sites for the large molecules, especially the heavy oil organic molecules to conduct the shape-selective reaction in the processes of petrochemical industry greatly encourage the chemical engineers. However, since the synthesis of such a molecular sieve requires large amounts of organic templates and auxiliary organic compounds such as cetyl trimethylammonium bromide (CTMAB), quaternary ammonium alkali and other organic compounds, and the resulting molecular sieve has so poor thermal stability (especially hydrothermal stability) that its crystal lattice can be retained in boiling water for only several hours or even shorter, it would be hard for them to have any value for practical applications.
Through the effort of recent years, some new mesoporous materials have been synthesized, but most of these materials are the improvements of MCM-41 which are, for example, synthesized by using new processes (U.S. Pat. Nos. 6,190,639, 6,096,287, 5,958,368, and 5,595,715, and Chinese Patent (Application) ZL 99103705.7, 96193321.6, and 95192999.2). Some hetero-atom substituted MCM-41 are synthesized (U.S. Pat. Nos. 6,193,943, 6,054,052, 6,042,807, 5,855,864, and 5,783,167, and Chinese Patent (Application) ZL.95105905.X, and 99107789.X) and thick wall MCM-41 is also synthesized (U.S. Pat. No. 6,193,943). However, the problem of the poor hydrothermal stability has not been substantively solved in these arts.
To overcome the shortages and problems of the above techniques, an object of the present invention is to provide a molecular sieve (hereinafter names it MPL-1), which has a character of mesoporous structure, larger and distribution concentrated pore diameters, larger specific surface and adsorption capacity, high thermal and hydrothermal stabilities. Meanwhile, a further object of the present invention is to provide a process for preparing such a molecular sieve.
The mesoporous molecular sieve provided by the present invention comprises at least three elements, i.e. phosphorus, aluminum, and oxygen, wherein the P2O5/Al2O3 molar ratio is 0.5-1.5, preferably 0.7-1.3, and most preferably 0.7-1.0, and has a specific X-ray diffraction pattern.
The molecular sieve according to the present invention has a X-ray diffraction pattern on which its strongest diffraction peak is at the position 2xcex8=1.5xc2x0-13.0xc2x0 with the units d-spacing greater than 4.0 nm, preferably 4.0 nm-6.0 nm. Particularly, the molecular sieve according to the present invention has substantively the same X-ray diffraction pattern as shown in FIG. 1.
The molecular sieve of the present invention has a pore diameter of 1.3 nm-10.0 nm, preferably 2.0 nm-10.0 nm, and most preferably 2.0 nm-5.0 nm.
The molecular sieve of the present invention may further contain elements Si and/or Ti, wherein the T/Al2O3 molar ratio is 0.01-2.0, preferably 0.01-1.0, wherein T represents Si and/or Ti.
Besides aluminum and/or titanium, the molecular sieve of the present invention may further contain one or more other metal elements. The molar ratio of said other metal(s) to alumina M/Al2O3=0.01-2.0, preferably 0.01-1.0, and most preferably 0.1-0.5, wherein M represents the other metal element(s).
The molecular sieve of the present invention has a pore volume of 0.30 ml/g-1.00 ml/g, preferably 0.40 ml/g-0.70 ml/g; and a specific surface area of 300 m2/g-1000 m2/g, preferably 500 m2/g-800 m2/g.
The molecular sieve of the present invention has excellent adsorption capacities towards benzene and water. Particularly, every 100 g of said molecular sieve has adsorption capacity towards benzene of more than 10 g, preferably 12 g-25 g at 25xc2x0 C. and PS/PO=0.016, and every 100 g of said molecular sieve has adsorption capacity towards water of more than 50 g, preferably 52 g-70 g at 25xc2x0 C. and PS/PO=0.026.
The molecular sieve of the present invention has higher thermal and hydrothermal stabilities. Its crystal lattice is not damaged after being calcined at 700xc2x0 C. for 2 h and its crystallinity is not substantively decreased after being heated in boiling water for 10 h.
The other metal element in addition to aluminum, which may be used in the molecular sieve of the present invention, is one or more selected from the group consisting of La, Ce, Ti, Ni, Co, Cr, Ca, Cu, Zn, Mg, and Fe.
The molecular sieve of the present invention may be prepared by a process comprising the steps of:
(a) mixing a template, an aluminum source, and a phosphorus source with water, stirring the mixture and adjusting the pH value of the mixture to 6-11, wherein the molar ratio of various materials is P2O5/Al2O3=0.5-1.5, preferably 0.7-1.3, and most preferably 0.7-1.0; H2O/Al2O3=50-500, preferably 100-400; R/Al2O3=0.2-2.0, preferably 0.3-1.0, where R is a template;
(b) crystallizing the resulting mixture of step (a) to form a precipitate, recovering and washing and drying the solid product to obtain the as-synthesised molecular sieve; and
(c) calcining the as-synthesised molecular sieve of step (b) to remove the template to obtain the mesoporous molecular sieve of the present invention.
In the above synthetic process, it is possible to selectively add, where necessary, one or more silicon sources and titanium sources to step (a) to allow the T/Al2O3 molar ratio in the mixture obtained in step (a) to be 0.01-2.0, preferably 0.01-1.0, more preferably 0.1-0.5. Furthermore, it is possible to selectively add, where necessary, other metal sources in addition to the aluminum sources to allow the M/Al2O3 molar ratio in the mixture obtained in step (a) to be 0.01-2.0, preferably 0.01-1.0, and most preferably 0.1-0.5, wherein M represents the other metal element(s).
In the above synthetic process of the present invention the aluminum source is one or more selected from the group consisting of active aluminas and their precursors, soluble aluminum salts and organic aluminium-containing compounds; said phosphorus source may be inorganic or organic compounds containing phosphorus, such as orthophosphoric acid, phosphorous acid, pyrophosphoric acid, phosphorus trichloride, phosphorus oxychloride, and phosphates, etc., preferably orthophosphoric acid; said silicon source is generally one or more selected from the group consisting of silica sol, white carbon black, water glass and ortho-silicate; the titanium source is one or more selected from the group consisting of TiO2, TiF4, TiCl4, TiOCl2, Ti(SO4)2, tetramethyl titanate, tetraethyl titanate, and tetrapropyl titanate, and the derivatives thereof.
In the above process, said other metal source other than aluminum prefers the soluble salts such as one or more metal-containing compounds selected from the group consisting of the nitrate, sulfate, acetate and chloride of La, Ce, Ti, Ni, Co, Cr, Ca, Cu, Zn, Mg and Fe.
The template used in the above synthetic process may be represented by the general formula: R1R2R3R4NX, wherein R1, R2, R3, and R4 independently represent a substituting group, N represents element nitrogen or phosphorus, and X represents hydroxyl or halogen such as F, Cl, Br, or l. Besides, at least one substituting group among said R1, R2, R3, and R4 is a group containing 5 or more carbon atoms, such as cetyl trimethylammonium chloride (CTMAC), cetyl trimethylammonium bromide (CTMAB), octadecyl trimethylammonium salts. It is preferred that at least one substituting group among R1, R2, R3, and R4 contains one or more polar functional groups, which can be selected from a group consisting of amino, hydroxyl, carboxyl, sulfhydryl, aldehyde group, and halogens such as F, Cl, Br or l. The most preferred ones are phenethoxy-2-hydroxypropyl trimethylammonium chloride (PTMAC) and/or phenethoxy-2-hydroxypropyl trimethylammonium bromide (PTMAB) or a mixture of phenethoxy-2-hydroxypropyl trimethylammonium chloride (PTMAC) and/or phenethoxy-2-hydroxypropyl trimethylammonium bromide (PTMAB) with other organic compounds capable of serving as a template.
The pH value of said mixture in step (a) of the above process is preferably 7-10, and more preferably 7.5-9.0. The substances used to adjust the pH of the mixture may include any substance capable of adjusting acidity and alkalinity such as acids, alkalis or salts, preferably inorganic or organic alkalis such as sodium hydroxide, potassium hydroxide, aqueous ammonia, primary amines, secondary amines, tertiary amines, or quaternary ammonium alkali, more preferably quaternary ammonium alkali and/or aqueous ammonia.
In step (b) of the synthetic process of the present invention, said crystallization temperature is 100xc2x0 C.-200xc2x0 C., preferably 130xc2x0 C.-170xc2x0 C., and the crystallization time is 4 h-240 h, preferably 24 h-96 h; said calcination temperature in step (c) is 450xc2x0 C.-700xc2x0 C., preferably 500xc2x0 C.-650xc2x0 C., and calcination time is 2 h-24 h, preferably 4 h-8 h.